1. Field of the Invention
The present invention relates generally to semiconductor fabrication methods and, more particularly, to fabrication of an ultra thin image sensor package structure.
2. Description of Related Art
Personal devices that employ image sensors are rapidly proliferating. Personal data assistants (PDAs) and cell phones now join digital cameras and camcorders in the family of products that frequently include image sensing capabilities. Because of their small size and the requirement for portability, such products benefit greatly from the existence of miniature electronics. Any opportunity to reduce the size, weight, and power consumption of image sensing electronic components accrues to the benefit of these personal devices and, therefore, to the public in general in terms of convenience and utility.
FIG. 1 is a cross-sectional diagram of a prior-art image sensor package 10 that may appear in a device such as a digital camera. This package comprises an image sensor chip 15 that is supported by a leadframe 20. Leads 25 on the leadframe 20 are connected to a plurality of bonding pads 30 on the image sensor chip 15 by a plurality of wire loops 35. A transparent lid 40 disposed on a surface of the image sensor package 10 allows light to reach an active light-sensitive surface on the image sensor chip 15. The entire assembly is encapsulated in a plastic package 45 that protects the internal components from dust, moisture, and mechanical damage.
Each of the components just introduced contributes to the thickness and weight of the image sensor package 10. In particular, a bottom portion 50 of the plastic package 45, the leadframe 20 that supports the image sensor chip 15, the image sensor chip 15 itself, the height of the wire loops 35, and the thickness of the transparent lid 40 all contribute to a total thickness of the device. Each of these components has a weight as well that contributes to the total weight of the device. Further, the bottom portion 50 of the plastic package 45 may act as a thermal insulator that undesirably tends to impede the dissipation of heat generated by the image sensor chip 15.
FIG. 2 is a cross-sectional diagram of another prior art image sensor package 60 packaged in, for example, a quad flat pack (QFP). This exemplary device also comprises an image sensor chip 65 that is supported by a leadframe 70. As before, leads 75 on the leadframe 70 are connected to bonding pads 80 on the image sensor chip 65 by wire loops 85. A transparent lid 90 disposed on a surface of the package allows light to reach an active light-sensitive surface on the image sensor chip 65. The entire assembly is encapsulated in a plastic package 95 that protects the internal components from dust, moisture, and mechanical damage. It should be noted that the leadframe 70, for example, contributes to the thickness and weight of the image sensor package 60.
As the capabilities of image sensing products continue to expand, while the demand for smaller and more lightweight products expands, a need continues in the prior art for image sensor packages that are relatively thin and lightweight compared to existing packages. A further need exists for packages that can efficiently dissipate heat generated by image sensor chips.